1. Field of the Invention
The present invention relates to an electrochemical cell such as a battery of button or coin type, or a capacitor.
2. Description of the Background Art
An electrochemical cell, such as a primary battery, a secondary battery or a capacitor of coin or button type, employed as a backup auxiliary power source for clock and memory functions of portable equipment, is usually utilized with two terminals mounted as positive and negative poles of the battery.
With the recent progress in size reduction of components, there now are mounting boards with holes for terminals which are inserted in the top surface and soldered from the rear surface of the board (for example, cf. patent reference 1). Also, in a type widely employed recently, an electrochemical cell to which terminals are attached beforehand are simply placed on a board, and solder-plated end portions of the terminals are fixed by soldering to the top side of the board (for example cf. patent reference 2). FIG. 2 shows a lateral view of a conventional electrochemical cell having two terminals. As illustrated therein, the electrochemical cell is formed by hermetically sealing a positive pole can 103 and a negative pole can 105 with a gasket 108, and the positive-pole can 103 and a positive pole terminal 104 are fixed at a laser weld point 101. The negative pole can 105 and a negative pole terminal 110 are fixed at a laser welded point 102. The positive pole terminal 104 and the negative pole terminal 110 are provided respectively with a plated layer 109 and a plated layer 107. Since the soldering to a circuit board 111 is executed at these two terminals, there is required a mounting area corresponding to such two terminals. In case the electrochemical cell is employed as a memory backup power source, there is often employed a method of welding terminals suited for soldering to the electrochemical cell and then soldering the cell to the circuit board together with a memory device. The soldering to the circuit board has been executed with a soldering iron, but, as a result of reduction in dimensions and expansion of functions of the product, it has become necessary to mount a larger number of electronic components within a limited area circuit board and it has become difficult to secure space for inserting the soldering iron. Also, there is demand for an automated process for soldering, for cost reduction.
Therefore, a reflow soldering process is currently employed, by applying a solder cream or the like in the location on the circuit board to be soldered and placing the component to be attached on that, or else providing a small solder ball to a part of the circuit board to be soldered after a component is placed on the circuit board, and then passing the circuit board, bearing the component thereon, through an oven of such a high temperature that the part to be soldered assumes a temperature equal to or higher than the melting point of solder, for example 200 to 260° C., thereby melting the solder and achieving the soldering operation.
[Patent Reference 1] JP-A No. 61-18568 (FIGS. 1 and 2)
[Patent Reference 2] JP-A No. 11-40174 (FIG. 1)
As a result of a size reduction of the equipment in which an electrochemical cell is mounted, a further reduction in the mounting area is also demanded for the electrochemical cell. However, even if the electrochemical cell itself can be made smaller, it has been difficult to reduce the dimension of the terminals and still secure a stability and a peeling strength of soldering. Also the conventional electrochemical cell is provided with two terminals, namely a positive pole terminal and a negative pole terminal, thus requiring a large mounting area.
Also, the conventional terminal is plated with a Pb-containing solder on its end portion which is to be soldered to the circuit board, but a reduction in Pb, which is an environmental pollutant, is demanded. On the other hand, in case Sn or a Sn-alloy, free from Pb, is employed for such plating, whiskers are generated by the heat at the terminal welding and cause short circuiting.